Patent Application
20140206907
This disclosure relates to a process for producing polyether glycols. More particularly, the disclosure relates to an improved process for preventing pressure build up across a catalyst separation system in a polyether polyol reactor.
Homopolymers of THF, also known as polytetramethylene ether glycols (PTMEG), are well known for use in spandex, polyurethanes and other elastomers. These homopolymers impart superior mechanical and dynamic properties to polyurethane elastomers, fibers and other forms of final products. Copolymers of THF and at least one other cyclic ether, also known as copolyether glycols, are known for use in similar applications, particularly where the reduced crystallinity imparted by the incorporation of the second cyclic ether may improve certain dynamic properties of a polyurethane which contains such a comonomer as a soft segment. Among the other cyclic ethers used for this purpose are ethylene oxide and propylene oxide. Copolyether glycols having a higher molar incorporation of alkylene oxide are desirable for higher polarity and hydrophilicity as well as improved dynamic properties, for example low temperature flexibility. Copolyether glycols having lower crystallinity are also desirable for use in manufacturing polyurethane and other elastomer which contains such a copolymer as a soft segment.
U.S. Pat. No. 4,120,903 discloses a process for making poly tetramethylene ether glycol (PTMEG) that involves first making the tetramethylene oxide polymer terminated by an acetate ester group (PTMEA). The process makes PTMEA by reacting tetrahydrofuran (THF) with acetic anhydride (ACAN) in a slurry reactor in the presence of a superacid catalyst. This reaction is carried out in a continuous stirred tank reactor (CSTR).
Particularly, U.S. Pat. No. 4,120,903 discloses the polymerization of THF using a polymer containing alpha-fluorosulfonic acid groups as a catalyst and water or 1,4-butanediol as a chain terminator. The nature of the catalyst permits its reuse and thereby eliminates disposal problems. In addition, the catalyst's lack of solubility in the reaction mass makes it desirable to separate the catalyst from the product at the end of the polymerization reaction. This very low solubility also minimizes loss of catalyst as the reaction proceeds.
The crude product is then withdrawn from the reactor through filters and the catalyst particles remain in the reactor for continued use. The filters are called “candle filters” because they protrude (like candles) upwardly into the CSTR. PTFE cloth filters were used for the filters because it was believed that the superacid catalyst would corrode a stainless steel filter and cause it to mechanically fail or that the superacid would leach metal from the stainless steel filters, thus contaminating and destroying the catalyst.
Accordingly, the inventors of the present application originally tried filters consisted of sheets of perforated polytetrafluoroethylene (PTFE, for example Teflon® brand PTFE). However, during filtering the slurry liquid in the reactor, the PTFE cloth filters clogged because they collected an excessive amount of catalyst fines. Further complicating the problem, it was discovered that the solid superacid catalyst swelled to different sizes depending upon the molecular weight of the PTMEA product. Thus sizing the PTFE cloth filters to allow catalyst fines to pass and unbroken catalyst particles to remain in the reactor was unsuccessful.
In addition, catalyst filtration was attempted with wire filters with round cross-section. However, the filters were clogged by catalyst fines and are corroded, causing them to mechanically fail.
Another operational design problem is maintaining effective catalyst filtration with little to no pressure differential across the filtration system in the reactor. The reactor is a continuously stirred tank reactor fitted with a rotating agitator to keep the heterogeneous reaction mass fluidized for maximum contact. The heat generated in the exothermic reaction is removed using evaporative cooling of the low volatile reactor contents using a vacuum system. The vacuum condition in the reactor results in significantly reduced driving force necessary to push the product of the reactor out through the candle filters. These unique operation conditions and design requirements cause the exit flow to essentially rely on gravity and the hydrostatic head of the reactor. If the candle filters provide too much resistance, pressure will build in the filters and it will limit the ability for flow and thus the production rate of the reactor will be decreased. One way to minimize this problem is to allow for periodic backflushing of the filters. However, this process is time consuming and costly, and is consequently not a desired remedy.
Therefore, there is a need for a catalyst separation system that can operate under a low pressure differential, does not require frequent backflush and allows catalyst fines to pass to prevent plugging.
The present invention relates to a process for producing a polyether polyol product with a catalyst separation system that effectively operates under a low pressure differential, does not require frequent backflush and allows catalyst fines to pass to prevent plugging of the system.
The catalyst separation system is comprised of a plurality of filters. Each filter is comprised of a plurality of spaced-apart elements. The spaced-apart elements are designed to allow the catalyst fines to pass through the filters and prevent a pressure build up across the catalyst separation system. This particular feature of the present invention enables the catalyst separation system to function under a low pressure differential while allowing the reactor to run at a higher production throughput. It also eliminates the need for excessive backflushing of the filters to unclog plugging. An embodiment of the process comprises the steps of:
(a) feeding reactants that comprise (1) a monomer or (2) a monomer and a co-monomer(s) to be polymerized to form the polyether polyol into a continuous feed reactor, said reactor having a catalyst suspended in solution;
(b) reacting the monomer or co-monomers in the presence of the catalyst to form a product stream comprising a polyether polyol product, unreacted reactants, catalyst fines and suspended catalyst;
(c) flowing the product stream from step (b) into a catalyst separation system within the reactor, wherein the catalyst separation system is comprised of a plurality of filters, wherein each filter comprises an outer surface and an inner surface defined by a plurality of spaced-apart elements, wherein the outer surface of the spaced-apart elements faces the suspended catalyst and is wider than the inner surface of the spaced-apart elements, and wherein the distance between the spaced-apart elements is smaller than the minor dimension of the largest 80% by weight of the suspended catalyst; and
(d) recovering the filtered polyether polyol product, unused reactants and catalyst fines from the reactor outlet.
In one embodiment, the distance between the spaced-apart elements is between 10% and 60% of the minor dimension of the largest 80% by weight of the catalyst.
In another embodiment, the spaced-apart elements do not intersect. In a particular embodiment, the spaced apart elements are formed from a single, spiraling element.
In another embodiment, the spaced-apart elements are wires having a wedged cross-section.
In another embodiment, the spaced-apart elements can have a trapezoidal cross-section, a triangular cross-section or a semi-circle cross-section.
In another embodiment, the distance between the spaced-apart elements is selected to allow the catalyst fines to pass. The distance between the spaced-apart elements can be selected to pass the catalyst fines having a minor dimension of less than 0.2 mm.
In another embodiment, the spaced-apart elements comprise metal that corrodes more slowly than carbon steel in the presence of an acidic ion exchange resin under polymerization reaction conditions.
In another embodiment, the filter is a cylindrical filter. The cylindrical filter may have extensive spaced-apart elements linearly extend in a radial direction of the cylindrical filter, and are arranged around a circumferential direction of the cylindrical filter in a uniform interval. It is also contemplated that the spaced-apart elements may linearly extend in an axial direction of the cylindrical filter.
In another embodiment, the catalyst is a heterogeneous superacid catalyst selected from the group consisting of zeolites optionally activated by acid treatment, sheet silicates optionally activated by acid treatment, sulfate-doped zirconium dioxide, supported catalysts comprising at least one catalytically active oxygen-containing molybdenum and/or tungsten compound or a mixture of such compounds applied to an oxidic support, polymeric catalysts which contain sulfonic acid groups, and combinations thereof. In another embodiment, the catalyst is a polymeric catalyst which contains sulfonic acid groups. In another embodiment, the polymeric catalyst comprises a perfluorosulfonic acid resin. In another embodiment, the superacid catalyst swells in the presence of at least one of the reactants.
In yet another embodiment, the monomer to be polymerized is tetrahydrofuran (THF). In another embodiment, the co-monomer to be polymerized is an alkylene oxide selected from a group consisting of ethylene oxide, 1,2-propylene oxide, 1,3-propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, 1,3-butylene oxide and combinations thereof.
In another embodiment, the polyether polyol product is polytetramethylene ether acetate (PTMEA). In another embodiment, the polyether polyol product is a copolyether glycol comprising a copolymer of THF and an alkylene oxide, wherein the alkylene oxide is selected from a group consisting of ethylene oxide, 1,2-propylene oxide, 1,3-propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, 1,3-butylene oxide and combinations thereof.
The present invention relates to a process for producing a polyether polyol product with a catalyst separation system that effectively operates under a low pressure differential, does not require frequent backflush and allows catalyst fines to pass to prevent plugging of the system.
All patents, patent applications, test procedures, priority documents, articles, publications, manuals, and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted.
The term “polymerization”, as used herein, unless otherwise indicated, includes the term “copolymerization” within its meaning.
The term “PTMEG”, as used herein, unless otherwise indicated, means poly(tetramethylene ether glycol). PTMEG is also known as polyoxybutylene glycol.
The term “copolyether glycol”, as used herein in the singular, unless otherwise indicated, means copolymers of tetrahydrofuran and at least one other alkylene oxide, which are also known as polyoxybutylene polyoxyalkylene glycols. An example of a copolyether glycol is a copolymer of tetrahydrofuran and ethylene oxide. This copolyether glycol is also known as poly(tetramethylene-co-ethyleneether) glycol. The copolymers produced in the present process are random copolymers in nature.
The term “THF”, as used herein, unless otherwise indicated, means tetrahydrofuran and includes within its meaning alkyl substituted tetrahydrofuran capable of copolymerizing with THF, for example 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, and 3-ethyltetrahydrofuran.
The term “alkylene oxide”, as used herein, unless otherwise indicated, means a compound containing two, three or four carbon atoms in its alkylene oxide ring. The alkylene oxide can be un-substituted or substituted with, for example, linear or branched alkyl of 1 to 6 carbon atoms, or aryl which is un-substituted or substituted by alkyl and/or alkoxy of 1 or 2 carbon atoms, or halogen atoms such as chlorine or fluorine. Examples of such compounds include ethylene oxide (EO); 1,2-propylene oxide; 1,3-propylene oxide; 1,2-butylene oxide; 1,3-butylene oxide; 2,3-butylene oxide; styrene oxide; 2,2-bis-chloromethyl-1,3-propylene oxide; epichlorohydrin; perfluoroalkyl oxiranes, for example (1H, 1H-perfluoropentyl) oxirane; and combinations thereof.
As shown in
Also as shown in
Suitable heterogeneous acid catalysts for use herein include, by way of example but not by limitation, zeolites optionally activated by acid treatment, sheet silicates optionally activated by acid treatment, sulfate-doped zirconium dioxide, supported catalysts comprising at least one catalytically active oxygen-containing molybdenum and/or tungsten compound or a mixture of such compounds applied to an oxidic support, polymeric catalysts which contain sulfonic acid groups (optionally with or without carboxylic acid groups), and combinations thereof. The supported catalyst could also include heteropolyacids, heteropolyacid salts, and mixtures of heteropolyacids such that the catalysts are not soluble under the reaction conditions employed here.
Among the suitable polymeric catalysts which contain sulfonic acid groups, optionally with or without carboxylic acid groups, are those whose polymer chains are copolymers of tetrafluoroethylene or chlorotrifluoroethylene and a perfluoroalkyl vinyl ether containing sulfonic acid group precursors (again with or without carboxylic acid groups) as disclosed in U.S. Pat. Nos. 4,163,115 and 5,118,869 and as supplied commercially by E. I. du Pont de Nemours and Company under the tradename Nafion® resin catalyst. Such polymeric catalysts are also referred to as polymers comprising alpha-fluorosulfonic acids. An example of this type of catalyst for use herein is a perfluorosulfonic acid resin, i.e. it comprises a perfluorocarbon backbone and the side chain is represented by the formula —O—CF2CF(CF3)-O—CF2CF2SO3H. Polymers of this type are disclosed in U.S. Pat. No. 3,282,875 and can be made by copolymerization of tetrafluoroethylene (TFE) and the perfluorinated vinyl ether CF2═CF—O—CF2CF(CF3)-O—CF2CF2SO2F, perfluoro (3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) (PDMOF), followed by conversion to sulfonate groups by hydrolysis of the sulfonyl fluoride groups and ion exchanged as necessary to convert them to the desired acidic form. See also U.S. Pat. No. 4,139,567 for a description of perfluorosulfonic acid resin catalyst useful herein.
The polymeric heterogeneous catalysts which can be employed according to the present invention can be used as shaped bodies, for example in the form of beads, cylindrical extrudates, spheres, rings, spirals, or granules. In the exemplary embodiment shown in
Referring again to
The design of the filter 100 for the purpose of preventing pressure build-up across the catalyst separation system 40 will now be discussed in greater detail. As shown in
Referring to
Referring to
As shown in an arrow in
In an exemplary embodiment of the present invention, the tapered meshes may have a degree of taper, K. For a standard mesh filter design with no taper, the widths of 101a and 101b would be defined by d2=d1 and L2=L1.
In case of wedge wire design of a particular embodiment of the present invention, the widths are defined by d2>d1 and L2<L1 and the taper K is defined by d1 divided by d2.
The value of K is defined in the range of 0.1 to 1. Preferably, this range is 0.1 to 0.5 and more preferably equal to 0.3. In
When using the filter 100 shown in
In the exemplary embodiments illustrated in
Example 1 illustrates the increase of catalyst fines recovered when the catalyst separation system of the current invention is used over a traditional mesh filter. 150 g of wet used Nafion® resin catalyst (about 46.5 g if dried) from the INVISTA LaPorte THF plant was loaded into a flask. The catalyst is in the form of symmetrical cylindrical pellets with an average length and diameter of about 0.8 to 1.0 mm. This used catalyst contains fines that naturally build up in the reaction over several months. The flask was then loaded with THF (2682 g), stirred and drawn out through the filter element at a constant rate and ambient temperature. The flask was reloaded 3 times and each time it was stirred and drawn out through the filter element the same way. In test 1, the filter element was a 4.4 cm2 construction consisting of four 250-micron layers over three 500-micron layers of PTFE mesh fabric, the multilayer construction being needed for back-flush strength in a large scale embodiment. The fines that passed through the element were collected in a settler and partly in the final collection flask. The fines were found to have a minor dimension size in the range of about 0.035 to about 0.280 mm, and an average minor dimension size of about 0.150 mm. The results are summarized in Table 1.
In test 2, the filter element was a 3 cm2 rectangular piece of stainless steel type 304 metal wedge wire filter with a 0.279 mm gap (this distance between the spaced-apart elements is within 10%-60% of the minor dimension of the largest 80% by weight of the suspended catalyst, which is between 0.8-1.0 mm), an outer wedge surface width of 1.194 mm and an inner surface wedge width of 0.597 mm, as is used in a particular embodiment of the present invention. The fines that passed through the element were collected in a settler and partly in the final collection flask. The results are summarized in Table 2.
The fines passed in each test were broken pieces of catalyst fines. No whole catalyst particles passed during the testing. In Test 1, 0.05 wt % of the catalyst loaded passed through the mesh element. In Test 2, 0.25 wt % of the catalyst loaded passed through the wedge wire element. The tests thus showed 5 times as many fines passed using the wedge wire element as using the multilayer mesh element. Thus, the wedge wire filter used with the catalyst separation system of the present invention is more efficient at purging the catalyst fines that can cause back pressure on the filter.
Prevention of pressure build-up across a catalyst separation system in a polyether polyol reactor is accomplished by feeding reactants that comprise a monomer or co-monomers to be polymerized to form the polyether polyol into a continuous feed reactor, said reactor having a catalyst suspended in solution. At least a portion of the monomer or co-monomers are reacted in the presence of the catalyst to form a product stream comprising a polyether polyol product, unreacted reactants, catalyst fines and suspended catalyst.
The product stream then flows into a catalyst separation system within the reactor, wherein the catalyst separation system is comprised of a plurality of filters, wherein each filter comprises an outer surface and an inner surface defined by a plurality of spaced-apart elements, wherein the outer surface of the spaced-apart elements faces the suspended catalyst and is wider than the inner surface of the spaced-apart elements, and wherein the distance between the spaced-apart elements is smaller than the minor dimension of the largest 80% by weight of the suspended catalyst.
The filtered polyether polyol product, unreacted reactants and catalyst fines are then recovered from the reactor outlet.
The process of Example 2 is repeated with additional steps. In this example, the distance between the spaced-apart elements is between 10% and 60% of the minor dimension of the largest 80% by weight of the catalyst.
The process of Example 3 is repeated with additional steps. In this example, the spaced-apart elements do not intersect.
The process of Example 4 is repeated with additional steps. In this example, the spaced apart elements are formed from a single, spiraling element.
The process of Example 5 is repeated with additional steps. In this example, the spaced-apart elements are wires having a wedged cross-section.
The process of Example 6 is repeated with additional steps. In this example, the spaced-apart elements have a trapezoidal cross-section, a triangular cross-section or a semi-circle cross-section.
The process of Example 7 is repeated with additional steps. In this example, the distance between the spaced-apart elements is selected to allow the catalyst fines to pass.
The process of Example 8 is repeated with additional steps. In this example, the distance between the spaced-apart elements is selected to pass the catalyst fines having a minor dimension of less than 0.2 mm.
The process of Example 9 is repeated with additional steps. In this example, the spaced-apart elements comprise metal that corrodes more slowly than carbon steel in the presence of an acidic ion exchange resin under polymerization reaction conditions.
The process of Example 10 is repeated with additional steps. In this example, the filter is a cylindrical filter.
The process of Example 11 is repeated with additional steps. In this example, the spaced-apart elements linearly extend in a radial direction of the cylindrical filter, and are arranged around a circumferential direction of the cylindrical filter in a uniform interval.
The process of Example 12 is repeated with additional steps. In this example, the spaced-apart elements linearly extend in an axial direction of the cylindrical filter, and are arranged around a circumferential direction of the cylindrical filter in a uniform interval.
The process of Example 13 is repeated with additional steps. In this example, the catalyst is a heterogeneous superacid catalyst selected from the group consisting of zeolites optionally activated by acid treatment, sheet silicates optionally activated by acid treatment, sulfate-doped zirconium dioxide, supported catalysts comprising at least one catalytically active oxygen-containing molybdenum and/or tungsten compound or a mixture of such compounds applied to an oxidic support, polymeric catalysts which contain sulfonic acid groups, and combinations thereof.
The process of Example 14 is repeated with additional steps. In this example, the catalyst is a polymeric catalyst which contains sulfonic acid groups.
The process of Example 15 is repeated with additional steps. In this example, the polymeric catalyst comprises a perfluorosulfonic acid resin.
The process of Example 16 is repeated with additional steps. In this example, wherein the superacid catalyst swells in the presence of at least one of the reactants.
The process of Example 17 is repeated with additional steps. In this example, the monomer to be polymerized is tetrahydrofuran (THF).
The process of Example 18 is repeated with additional steps. In this example, the co-monomer to be polymerized is an alkylene oxide selected from a group consisting of ethylene oxide, 1,2-propylene oxide, 1,3-propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, 1,3-butylene oxide and combinations thereof.
The process of Example 19 is repeated with additional steps. In this example, the polyether polyol product is polytetramethylene ether acetate (PTMEA).
The process of Example 20 is repeated with additional steps. In this example, the polyether polyol product is a copolyether glycol comprising a copolymer of THF and an alkylene oxide, wherein the alkylene oxide is selected from a group consisting of ethylene oxide, 1,2-propylene oxide, 1,3-propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, 1,3-butylene oxide and combinations thereof.
It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt % to about 5 wt %, but also the individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. The term “about” can include ±1%, ±2%, ±3%, ±4%, ±5%, ±8%, or ±10%, of the numerical value(s) being modified. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.
While the illustrative embodiments of the invention have been described with particularity, it will be understood that the invention is capable of other and different embodiments and that various other modifications will be apparent to and may be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims hereof be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains.
This application claims the benefit of U.S. Provisional Application No. 61/503,689, filed Jul. 1, 2011, which is incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/43737 | 6/22/2012 | WO | 00 | 3/27/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61503689 | Jul 2011 | US |
